With increasing needs for alternative energy sources, turbines harnessing wind and water energy are gaining in popularity. A turbine harnesses mechanical power, characterized by torque and speed of a rotary movement imparted its blades by an air flow or by a water flow. The turbine is coupled with a generator capable of transforming a part of that mechanical power into electric power. Many existing generators use a brushless design. A brushless generator has no commutating electric device connected to its rotor. This simple design, in which a rotary magnetic field is provided by permanent magnets within the rotor, requires limited maintenance.
A specific generator configuration comprises a disk shaped rotor positioned alongside a disk shaped stator. The disk shaped rotor has permanent magnets placed side by side in a ring configuration positioned within its periphery. The stator has multiple coils positioned in a plane of the stator, along its periphery. Upon rotation of the rotor, a magnetic field of its permanent magnets energizes the coils of the stator to produce current by electromagnetic induction. An equivalent motor configuration may be used, in which an electric source energizes the coils of the stator, creating an electromagnetic field that induces a rotating force on the rotor.
A disk shaped brushless motor/generator therefore has a generally flat shape, having a radius larger than its depth. It may be used in various applications in the field of renewable energy where it may for example accommodate a turbine shape. As an example, a vertical axis wind turbine, commonly known as a Darrieus turbine, may benefit from the simplicity of a flat, disk shaped generator, the turbine being directly attached to the disk shaped rotor. This type of generator may provide electric power at low rotational speed, using a direct drive without the need for a gearbox system.
When used underwater, classic electric motors/generators are sealed in order to prevent intrusion of any fluid that could potentially damage the stator and the rotor. A motor/generator is usually coupled to a mechanical working load or driving device, such as a turbine, via a rotating shaft used to transmit mechanical power. A sealing dispositive positioned around the shaft at a point where the shaft protrudes from a chassis of the motor/generator may eventually wear out and allow fluid leakage into the chassis. Maintenance of the sealing dispositive is thus required to prevent any damage to internal components of the motor/generator.
Although some motors/generators may have their internal components designed to withstand the presence of a fluid within their chassis, ferrous particles that may be present inside the fluid may be magnetically attracted in the chassis and may accumulate on internal walls of the chassis. This may damage the motors/generators, especially in the case of rotors having permanent magnets. As an example, a hydrokinetic turbine having its electric generator submerged into water and having a shaft directly coupled with a turbine may, due to the ongoing rotation of the shaft, wear out a sealing dispositive, creating an opening allowing water to reach inside the chassis. Intrusion of water will sooner or later occur, without ongoing proper maintenance.
Therefore, there is a need for transmitting power, torque or force between a rotating shaft and a motor or a generator while preventing any fluid leakage into a motor or generator chassis.